BT817AKTF 查看數據表（PDF） - Unspecified

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BT817AKTF

VideoStream™ Decoders

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Bt819A/7A/5A

FUNCTIONAL DESCRIPTION

Functional Overview

Scaling and Cropping

The Bt819A can reduce the video image size in both horizontal and vertical direc-

tions independently using arbitrarily selected scaling ratios. The X and Y dimen-

sions can be scaled down to one-fourteenth of the full resolution. Horizontal

scaling is implemented with a six-tap interpolation filter while two-tap interpola-

tion is used for vertical scaling with a line store. The Bt817A and Bt815A support

vertical scaling by line-dropping.

The video image can be arbitrarily cropped by programming the ACTIVE flag

to reduce the number of active scan lines and active horizontal pixels per line.

The Bt819A, Bt817A and Bt815A also support a temporal decimation feature

that reduces video bandwidth by allowing frames or fields to be dropped from a

video sequence at regular but arbitrarily selected intervals.

Input Interface

Analog video signals are input to the Bt819A/7A/5A via a three-input multiplexer

that can select between three composite source inputs or between two composite

and a single S-video input source. When an S-video source is input to the Bt819A,

the luma component is fed through the input analog multiplexer, and the chroma

component is fed directly into the C input pin (the Bt815A does not support S-vid-

eo input). An automatic gain control circuit enables the Bt819A/7A/5A to compen-

sate for reduced amplitude in the analog signal input.

The clock signal interface consists of two pairs of pins for crystal connection

and two clock output pins. One pair of crystal pins is for connection to a 28.64

MHz (8*NTSC Fsc) crystal which is selected for NTSC operation. The other is for

PAL operation with a 35.47 MHz (8*PAL Fsc) crystal. Either of the two crystal

frequencies can be selected to generate CLKX1 and CLKX2 output signals.

CLKX2 operates at the full crystal frequency (8*Fsc) whereas CLKX1 operates at

half the crystal frequency (4*Fsc). Either fundamental or third harmonic crystals

may be used. Alternatively, CMOS oscillators may be used.

Output Interface

The Bt819A’s output interface can be set up to support two different configura-

tions: the Synchronous Pixel Interface (SPI) and the Asynchronous Pixel Interface

(API). The Bt817A and Bt815A support the Synchronous Pixel Interface only.

Both the SPI and the API can support a YCrCb 4:2:2 data stream over a 16-bit-

wide path. The SPI also supports an 8-bit path. When the pixel output port is con-

figured to operate 8 bits wide, 8 bits of chrominance data are output on the first

clock cycle followed by 8 bits of luminance data on the next clock cycle for each

pixel. Two clocks are required to output one pixel in this mode, thus a 2x clock is

used to output the data.

In SPI mode, the Bt819A/7A/5A output interface is similar to the Bt812 inter-

face. The Bt819A/7A/5A outputs all horizontal and vertical blanking pixels in ad-

dition to the active pixels synchronous with CLKX1 (16-bit mode) or CLKX2

(8-bit mode). It is also possible to insert control codes into the pixel stream using

chrominance and luminance values that are outside the allowable chroma and luma

ranges. These control codes can be used to flag video events such as ACTIVE,

HRESET, and VRESET. Decoding these video events downstream enables the vid-

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